Field emission devices are known and commonly comprised of electron emitters which emit electrons into a free-space (vacuum) region by means of an induced electric field near the surface of the electron emitter. The electric field in many instances is realized by providing an extraction electrode (gate electrode) in close proximity to the electron emitter and applying a suitable potential therebetween. Emitted electrons are commonly, although not necessarily, collected by a distally disposed anode. However, in many instances field emission devices are identified as electron emitters with associated extraction electrode only. In many applications it is desirable to effect a means to control the field emission device electron emission.
It is known that by providing a select voltage between the extraction electrode of a field emission device and the electron emitter that the electron emission from the electron emitter will be prescribed in accordance with the electric field induced at the emitting surface of the electron emitter in accordance with the Fowler-Nordheim relation which may be generally given as: EQU J=AE.sup.2 /.0.exp [B.0..sup.3/2 /E]
In the above relationship it is seen that the current density, J, from the electron emitter is a strong function of the induced electric field, E, which is directly related to an applied extraction voltage.
A technique employed to effect electron emission control of field emission devices (FEDs) is to provide a controllable determined current source to the electron emitter of each field emission device. By determining the available current to each selected field emission device one need not be concerned with fabrication variations as the voltage between the extraction electrode and the electron emitter will assume any required value (within the limits established by attendant voltage sources) to deliver the determined current. However, known methods of realizing determined current source control do not provide for high FED to FED isolation due to the X-Y addressing schemes. Typically, an array of FEDs will be made operable by operably coupling a determined current source to each of a plurality of columns while each row of a plurality of rows of the array of FEDs is selectively energized with a suitable potential. Another shortcoming of prior art techniques is that significant displacement currents are required to charge/discharge an associated line capacitance as each row is selectively, cyclically energized (as may be the case in FED display applications) to a voltage on the order of from 50 to 150 Volts.
Accordingly, there exists a need for a method and field emission device control circuitry which overcomes at least some of these shortcomings.